Technical note EPR identi®cation of irradiated Monascus purpureus red pigment Octavian G. Duliu a, *, Mariana Ferdes b , Ovidiu S. Ferdes c a University of Bucharest, Department of Atomic and Nuclear Physics, Ma Ägurele, P.O. Box MG-11, RO-76900, Bucharest, Romania b Institute for Food Chemistry, str. Ga Ãrlei nr. 1, RO-71576, Bucharest, Romania c National Institute for Lasers, Plasma and Radiation Instruments, Ma Ägurele, P.O. Box MG-36, RO-76900, Bucharest, Romania Received 25 March 1998; received in revised form 22 January 1999; accepted 24 January 1999 Abstract Fresh red alimentary pigment extracted from Monascus purpureus fungus exhibits an intense EPR line consisting of a single, narrow line, attributed to a quinone radical. When irradiated with 7 MeV electrons or 60 Co g-rays, the amplitude of this line increased with the absorbed dose following a saturation exponential dependency up to 10 kGy. During annealing treatment (isothermal heating at 1008C) the irradiation centers decay exponentially with a half-life time of 2.30 min. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: EPR; Irradiated food; Identi®cation; Quinone; Monascus 1. Introduction Food irradiation with g-ray or high energy (7±10 MeV) electrons (Murrieta et al., 1996; Duliu et al., 1997; Desrosiers, 1996) at doses up to 10 kGy can destroy harmful bacteria and fungi with minor or even without impairments of the organoleptic properties of irradiated aliments. Due to the fact that in some countries the sale for human consumption of irradiated foodstus is restricted or even prohibited, the positive identi®cation of such kind of aliments represents an actual task of any state authority enabled to control the food quality. To accomplish this task, several techniques based upon the identi®cation of the various physico-chemical changes, which are induced during food irradiation, are currently used (DelinceÂe, 1991; Stevenson, 1993). Among them, Electron Paramagnetic Resonance (EPR) suggested itself as one of the most adequate methods due to its high sensitivity to unpaired elec- trons present in all free radicals generated during ir- radiation. Generally, EPR have been used for the investigation of the hard part of foodstus, able to retain for long time (up to 1 month) the irradiation free radicals (Wieser and Regulla, 1988; Ra and Agnel, 1989; Maloney et al., 1992; Ra and Stacker, 1996; Desrosiers, 1996). In the last decades, the interest for new natural pig- ments to be used in food industry is continuously growing. Among them there are red pigments pro- duced by the fungus Monascus purpureus, used for long time in dierent zones of Asia as natural color- ants to traditional dishes. It is used in foodstus prep- aration by replacing some traditional additives as E 120 (cochineal), E 252 (potassium nitrate) and E 249 (nitrites) (Berset, 1990, 1994; Fabre et al., 1993). The Monascus purpureus dye, consists of at least six pig- ments: anka¯avin, monascin, monascorubranine, mon- Radiation Physics and Chemistry 57 (2000) 97±101 0969-806X/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0969-806X(99)00305-9 www.elsevier.com/locate/radphyschem * Corresponding author. Fax: (+) 40 1 420 8625. E-mail address: odlu@scut.®zica.unibuc.ro (O. G. Duliu)